1. Field of the Invention
This invention relates to a meter and disposable device for measuring the concentration of an analyte in a biological fluid; more particularly, an apparatus for which the disposable device is a hollow frustum.
2. Description of the Related Art
Medical diagnosis often involves measurements on biological fluids, such as blood, urine, or saliva, that are taken from a patient. Generally, it is important to avoid both contamination of equipment and personnel with these fluids and to avoid contamination of the patient with fluids from others. Thus, there is a need for diagnostic devices that minimize the risk of such contamination.
Among the medical diagnostic devices that are in most widespread use today is the blood glucose monitor. In the U.S. alone, there are an estimated 14 million people with diabetes. In order to avoid serious medical problems, such as vision loss, circulatory problems, kidney failure, etc., many of these people monitor their blood glucose on a regular basis and then take the steps necessary to maintain their glucose concentration in an acceptable range.
Blood contamination is of concern when making a blood glucose measurement. For example, when using the most common types of whole blood glucose meters (photometric), the glucose determination is generally made from a blood sample that is applied to a test strip that is on the meter. To apply the patient's finger-stick blood sample, the patient's finger must be positioned above and near to the test strip in order to inoculate the test strip with the blood sample. There is a risk that the patient's finger may come into contact with a portion of the meter that is contaminated with blood from previous use by others, particularly when used in a hospital.
This risk to the patient is minimized if the test strip is inoculated before it is placed into the meter. This is the so called "off-meter dosing" approach. With this approach, the patient applies his blood sample to a reagent test strip as the first step in the measurement process. Then the strip is inserted into the meter. The patient's finger only comes into contact with a new (clean) disposable, which cannot be contaminated by another patient's blood. The finger never comes into contact with a contaminated portion of the meter. The approach of off-meter dosing has been used for some time, particularly with meters that operate photometrically, as well as in systems that measure hematocrit. A disadvantage of off-meter dosing is that the meter cannot take a measurement at or before "time-zero", the time when the sample was applied to the strip. In a photometric meter, a reflectance reading prior to strip inoculation permits the meter to correct for variations in strip background color and positioning. The meter can also determine time-zero more directly and more accurately, which facilitates accurate measurements. By contrast, time-zero may be difficult or impossible to determine if the strip is inoculated off-meter.
Although off-meter dosing reduces the contamination problem for the patient, the meter can still become contaminated with blood. There is thus a risk to others who may come into contact with the contaminated meter, such as workers in a hospital and meter repair technicians. Furthermore, if the patient is being assisted by a healthcare worker, that worker could come into contact with the patient's blood while removing the strip for disposal, after the test has been completed.
Meters that operate electrochemically typically use "remote dosing", in which the test strip is placed in the meter before inoculation, but the blood application point is remote from the meter surfaces that can become contaminated. For example, the Glucometer Elite.RTM. from Bayer Diagnostics and the Advantage.RTM. from Boehringer Mannheim incorporate electrodes with remote sample application. As with off-meter dosing, strip removal may also pose a risk for meters that use remote dosing.
A number of systems have been disclosed that are aimed at reducing the risk of contamination to a patient and/or to others in connection with diagnostic tests.
U.S. Pat. No. 4,952,373, issued Aug. 28, 1990, to Sugarman et al., discloses a shield that is designed to prevent excess liquid on diagnostic cartridges from being transferred to a monitor with which the cartridge is used. The shield is fabricated from thin plastic or metallic film and is attached to a cartridge that is generally the size of a credit card.
U.S. Pat. No. 5,100,620, issued Mar. 31, 1992, to Brenneman, discloses an inverse funnel shaped body with a central capillary tube to transport a liquid sample from a remote sample-application point to a test surface. The device can be used to transfer blood from a finger stick to a reagent film.
U.S. Pat. No. 3,991,617, issued Nov. 16, 1976, to Marteau d'Autry discloses a device that is used with a pipette intended to be used with disposable tips. The device provides a push button mechanism for ejecting the tip from the end of the pipette.
The common element of the above patents is that each of the devices disclosed addresses the risk of contamination that is posed by biological fluids and other potentially hazardous liquids.